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<H2><A NAME="SECTION006910000000000000000">
4.9.1 Codec Base Classes</A>
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<P>
The <tt class="module">codecs</tt> defines a set of base classes which define the
interface and can also be used to easily write you own codecs for use
in Python.

<P>
Each codec has to define four interfaces to make it usable as codec in
Python: stateless encoder, stateless decoder, stream reader and stream
writer. The stream reader and writers typically reuse the stateless
encoder/decoder to implement the file protocols.

<P>
The <tt class="class">Codec</tt> class defines the interface for stateless
encoders/decoders.

<P>
To simplify and standardize error handling, the <tt class="method">encode()</tt> and
<tt class="method">decode()</tt> methods may implement different error handling
schemes by providing the <var>errors</var> string argument.  The following
string values are defined and implemented by all standard Python
codecs:

<P>
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  <thead>
    <tr>
      <th class="left"  >Value</th>
      <th class="left"  >Meaning</th>
      </tr>
    </thead>
  <tbody>
    <tr><td class="left"   valign="baseline"><code>'strict'</code></td>
        <td class="left"  >Raise <tt class="exception">UnicodeError</tt> (or a subclass);
                    this is the default.</td></tr>
    <tr><td class="left"   valign="baseline"><code>'ignore'</code></td>
        <td class="left"  >Ignore the character and continue with the next.</td></tr>
    <tr><td class="left"   valign="baseline"><code>'replace'</code></td>
        <td class="left"  >Replace with a suitable replacement character;
                     Python will use the official U+FFFD REPLACEMENT
                     CHARACTER for the built-in Unicode codecs on
                     decoding and '?' on encoding.</td></tr>
    <tr><td class="left"   valign="baseline"><code>'xmlcharrefreplace'</code></td>
        <td class="left"  >Replace with the appropriate XML
                     character reference (only for encoding).</td></tr>
    <tr><td class="left"   valign="baseline"><code>'backslashreplace'</code></td>
        <td class="left"  >Replace with backslashed escape sequences
                     (only for encoding).</td></tr></tbody>
</table></div>

<P>
The set of allowed values can be extended via <tt class="method">register_error</tt>.

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<LI><A href="codec-objects.html">4.9.1.1 Codec Objects</a>
<LI><A href="stream-writer-objects.html">4.9.1.2 StreamWriter Objects</a>
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<LI><A href="stream-reader-writer.html">4.9.1.4 StreamReaderWriter Objects</a>
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<span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span>
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